ABS that forms a socket for the 8020
column to insert into. Wire routing for
the power switch and a charger
socket is done using a European-style
terminal strip and 14 ga wire.

The base design allows a full-size
( 14.1" screen) laptop to fit on the
back deck. The computer interfaces to
I/O through a Vanadium Labs ArbotiX
RoboController which is tucked in the
front of the base. The ArbotiX is used
as a co-processor — connected over
USB — which handles all real time
operations and passes serial
commands between the PC and
the arm/neck servos, as well as
implementing closed-loop PID control
of the mobile base. The base is shown
in Figure 4 without the top cover or
caster (which attaches to the top
cover).

The Torso and Head

laser-cut ABS. The pieces go together
using a collection of tabs and slots,
and are held in place using small
#4-40 corner brackets (Digi-Key P/N
621K-ND). This construction method
has proven to be quite reliable on
Maxwell, as well as in other projects.

The base uses a differential drive
setup with two DC gearhead motors
from Zagros Robotics ( www.zagros
robotics.com) which can power the
robot to speeds of up to 2 ft/sec.
The BaneBots ( www.banebots.com)
wheels provide a sturdy grounding,
with lots of grip. I had to drill out the
6 mm hubs on the wheels to attach
them properly to the 1/4" shafts on
the motors, but other than this quick
modification, the entire base can be
assembled with just a set of hex keys.
The battery is tie-strapped down, and
held in place by the same piece of

FIGURE 5. Maxwell disassembled
for transport and put into the Pelican
case. The base fits on top of this
(with a layer of foam in between).

Maxwell's torso is very
lightweight, constructed of three
pieces of 1" x 1" 8020 extruded
aluminum. The 8020 offers an easy
way to connect everything together
and to vary the height of the neck.
Maxwell's overall height is about
5 ft tall.

Three pieces of 8020 were used
with joining plates, so that Maxwell
could easily be broken down for
shipment or transport. By loosening
only six screws, the entire robot can
be broken down and fit into a Pelican
case. Figure 5 shows how the three
pieces are put into the case. A layer of
protective foam then covers the
components and the base is put on
top. This configuration has been
successfully shipped across the
country several times when traveling
to RoboGames and other events.

The head is composed of two
Dynamixel AX- 12 servos, and allows
the Asus Xtion RGBD camera to look
all around the robot. This sensor is
very much like the Microsoft Kinect,
but weighs much less and is much
smaller. Mounted on the back of the
torso is a big red button. This is the
emergency stop which cuts power to
all the servos and the base motors.
When building a robot this large, an
emergency stop is always a good idea